This invention relates to a fuel injection control method for supplying fuel through injection to a plurality of cylinders of an internal combustion engine, and more particularly to a method of this kind, which is adapted to perform a fail safe function in the event of occurrence of an abnormality in cylinder-discriminating means which determines the sequence of injections of fuel into the cylinders of the engine.
Among fuel supply control methods for electronically controlling the valve opening period of a fuel metering device of an internal combustion engine, for control of the quantity of fuel being supplied to the engine, a method has been proposed, e.g. by the assignee of the present application in Japanese Provisional patent publication (Kokai) No. 57-137633, which is adapted to first determine a basic value of the above valve opening period, i.e. the fuel supply quantity, as a function of engine rpm and intake pipe absolute pressure and then correcting the basic value thus determined by adding to and/or multiplying same by constants and/or coefficients being functions of parameters indicative of operating conditions of the engine such as engine coolant temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., while at the same time determining the timing of fuel injection into individual ones of the engine cylinders, from pulses of a crank angle position signal generated at predetermined crank angle positions of pistons within the individual engine cylinders, as well as from pulses of a cylinder-discriminating signal indicative of a predetermined crank angle position of a piston within a particular one of the engine cylinders, and driving fuel injection valves of the fuel metering device in accordance with the corrected fuel supply quantity and the determined fuel injection timing.
According to this control method, fuel is injected into a particular one of the engine cylinders in synchronism with a pulse of the crank angle position signal generated immediately after generation of each pulse of the cylinder-discriminating signal, and thereafter fuel is injected into the other engine cylinders in predetermined sequence in synchronism with subsequent pulses of the crank angle position signal.
In the same control method, due to a noise in cylinder-discriminating means for generating the cylinder-discriminating signal or omission of a pulse of the cylinder-discriminating signal as caused by malfunction of the cylinder-discriminating means, it can happen that an engine cylinder which corresponds to a first pulse of the crank angle position signal generated immediately after generation of a pulse of the cylinder-discriminating signal is different from the above particular engine cylinder. In such event, the sequence of fuel injections into the engine cylinders is changed so as to effect a first fuel injection into the above particular cylinder immediately after the generation of the above pulse from the cylinder-discriminating means and then effect fuel injections into the other cylinders in the above predetermined sequence.
However, if in the event of occurrence of a fault in the cylinder-discriminating means many abnormal pulses of the cylinder-discriminating signal occur, the frequency of the above changing of the fuel injection sequence increases, resulting in the phenomenon that some cylinders are twice supplied with fuel or two times as much as a required fuel quantity during one cycle of the engine, whereas some other cylinders are not supplied with fuel at all during the same cycle of the engine, which impedes smooth operation of the engine, greatly deteriorating the driveability of the engine.